[Freeswitch-users] Optimum codec list?

[Kristian Kielhofner]

Pete,

  As you saw the SIP MTU issue is a complex one; I get into that in my
blog post here:

http://blog.krisk.org/2013/09/apples-new-facetime-sip-perspective.html

  Needless to say I was "inspired" by Apple's use of HTTP-like SIP
body compression and it's now been implemented in Kamailio and
FreeSWITCH:

http://kamailio.org/docs/modules/4.1.x/modules/gzcompress.html
http://jira.freeswitch.org/browse/FS-5814

  So if you're using endpoints that support it you may be able to
include many more codecs without running into the IP fragmentation
issue. Also (as I note in my post) TCP suffers from far fewer issues
with fragmented IP packets in practice so you could just do that (or
both).

  Regarding codecs themselves, it's important to note that while
FreeSWITCH and other OSS projects support a wide range of codecs often
times commercial equipment does not. Unfortunately it's this
commercial equipment that's often at the actual ends of a call (IP
handset to LEC PSTN gateway, for example). The large scale media
gateways manufactured by Cisco, Sonus, and others in use by the
various LECs that operate the actual PSTN gateways often times only
support G711a, G711u, and G729. The use of any other codec requires
transcoding when using these gateways and transcoding is never a good
thing - it increases delay and reduces quality.

  Commercial IP handsets aren't much better. Your options for 8k
codecs are about the same as above and for wideband (16k or better)
you'll see support for G722 and others.

  WebRTC provided a huge shot in the arm for OPUS, which can actually
run from 8k - 48k. Unfortunately it's still not supported by any
existing media gateways or handsets that I'm aware of.

On Sat, Mar 22, 2014 at 9:40 AM, Pete Ashdown <pashdown at xmission.com> wrote:
> So considering I can't put every possible codec under the sun into
> codec_prefs, due to the aforementioned MTU limit on the SIP packet, what
> is considered an optimum set of codecs that fits with a wide
> compatibility base?
>
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-- 
Kristian Kielhofner